Merge branch 'ld/git-p4-tags-and-labels'

By Luke Diamand
* ld/git-p4-tags-and-labels:
git p4: fix unit tests
git p4: move verbose to base class
git p4: Ignore P4EDITOR if it is empty
git p4: Squash P4EDITOR in test harness
git p4: fix-up "import/export of labels to/from p4"
git p4: import/export of labels to/from p4
git p4: Fixing script editor checks